Occasionally ones appear and do not get noticed but by and large if they exist they will be on http://www.romhacking.net/?page=hacks&genre=&platform=10&game=&category=&perpage=50&title=&author=&hacksearch=Go (note not all are such hacks but several also improve other aspects of the game so well worth checking out and especially if you are looking at playing a RPG or strategy game).

Unlike many other SNES-to-GBA ports, the DKC trilogy has a lot more wrong with it than just palette issues. Many of the lighting effects were removed completely, and day/night transitions in DKC1 removed entirely. I found out later that most of the visual assets in the games were resized down by 25% of their original resolution. This process caused a huge loss of detail. And it makes palette swapping more difficult (and imo, not worth it). The palettes are uneven too, not brightened at a standard rate that is easy to fix.

Most other SNES games keep their sprites and background intact size-wise. And for the most part they still tend to be decent renditions of the original games (their flaws are nothing a little hacking can't fix). To compensate for the lower resolution, they just have a more narrow field of view on the screen. But in the DKC trilogy, Rare just scaled down all the visuals instead of doing it the smart way. The result is an ugly mess overall. I honestly hate what they did to these games. They're not the worst by any means because they're still perfectly playable gameplay-wise. But one expects more from Rareware.

Yoshi's Island could use some fixing, but i dunno whether anyone is still interested in this palette hack business anymore...

If you really want good portable versions of the DKC trilogy, i'd suggest a device that can easily emulate SNES well. I've an Android phone, and i know they make Android devices with controls (officially, the Xperia Play or else you could get one of those Yinlips devices as well). That would open up a good deal of great old systems as well as just SNES (there's even a pretty good GBA emulator for Android devices). The SNES versions of the DKC series can't be beaten in quality (except the VC releases which are emulated anyways). I avoid the GBA renditions even though they added content to all three of them. Even the extra world in DKC3 on GBA isn't worth what they did to it and the others (the new levels are hit or miss and the new "octopus" boss is really lame).